1. Field of the Invention
The present invention relates to a method of manufacturing a magnetic head for perpendicular magnetic recording that is used for recording data on a recording medium by means of a perpendicular magnetic recording system.
2. Description of the Related Art
The recording systems of magnetic recording/reproducing devices include a longitudinal magnetic recording system wherein signals are magnetized in a direction along the plane of the recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in a direction perpendicular to the plane of the recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of providing higher linear recording density, compared with the longitudinal magnetic recording system.
Magnetic heads for perpendicular magnetic recording typically have, as do magnetic heads for longitudinal magnetic recording, a structure in which a reproducing head having a magnetoresistive element (hereinafter, also referred to an MR element) for reading and a recording head having an induction-type electromagnetic transducer for writing are stacked on a substrate. The recording head includes a pole layer that produces a magnetic field in the direction perpendicular to the plane of the recording medium. The pole layer includes, for example, a track width defining portion having one end located in a medium facing surface that faces the recording medium, and a wide portion that is coupled to the other end of the track width defining portion and that is greater in width than the track width defining portion. The track width defining portion has a nearly uniform width.
For the perpendicular magnetic recording system, what mainly contributes to the improvement of recording density is the improvements of the recording medium and the recording head. What is required of the recording head to achieve higher recording density is the reduction of track width and the improvement of recording characteristics, in particular. On the other hand, as the track width is reduced, the recording characteristics, such as overwrite property which is a parameter indicating overwriting capability, suffer degradation. It is therefore required to achieve better recording characteristics as the track width is reduced. Here, the length of the track width defining portion taken in the direction perpendicular to the medium facing surface is called a neck height. The smaller the neck height, the better is the overwrite property.
A magnetic head for use in a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has the medium facing surface mentioned above. The medium facing surface has an air-inflow-side end and an air-outflow-side end. The slider is designed to slightly fly over the surface of the recording medium by means of an airflow that comes from the air-inflow-side end into the space between the medium facing surface and the recording medium. The magnetic head is typically disposed near the air-outflow-side end of the medium facing surface of the slider. In a magnetic disk drive, positioning of the magnetic head is performed by a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit about the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs according to the position of the magnetic head across the tracks.
In a magnetic disk drive of the perpendicular magnetic recording system, in particular, which exhibits better capability of writing on a recording medium compared with that of the longitudinal magnetic recording system, the skew mentioned above can cause problems such as a phenomenon in which, when data is recorded on a certain track, data stored on a track adjacent thereto is erased (the phenomenon is hereinafter referred to as adjacent track erasing), and unwanted writing between two adjacent tracks. To achieve higher recording density, it is required to suppress adjacent track erasing. Unwanted writing between two adjacent tracks affects the detection of servo signals for positioning the magnetic head and the signal-to-noise ratio of a reproduction signal.
As one of techniques for preventing the foregoing problems resulting from the skew, there is known a technique in which the end face of the track width defining portion located in the medium facing surface is formed into such a shape that the side located backward along the direction of travel of the recording medium (that is, the side located closer to the air inflow end of the slider) is shorter than the opposite side, as disclosed in, for example, U.S. Pat. No. 6,710,973 B2, U.S. Patent Application Publication No. US2003/0151850 A1, and U.S. Patent Application Publication No. US2006/0077589 A1. In the medium facing surface of a magnetic head, typically, the end farther from the substrate is located forward along the direction of travel of the recording medium (that is, located closer to the air outflow end of the slider). Therefore, the shape of the end face of the track width defining portion located in the medium facing surface mentioned above is such that the side closer to the substrate is shorter than the side farther from the substrate.
Consideration will now be given to a method of forming a pole layer in which the end face of the track width defining portion located in the medium facing surface has such a shape that the side closer to the substrate is shorter than the side farther from the substrate, as mentioned above. U.S. Pat. No. 6,710,973 and U.S. Patent Application Publication No. US2003/0151850 A1 each disclose a method including forming a groove in an inorganic insulating film by selectively etching the inorganic insulating film using a mask made of photoresist, and forming the pole layer in this groove. U.S. Patent Application Publication No. US2006/0077589 A1 discloses a method including forming a nonmagnetic conductive layer on a nonmagnetic layer, forming an opening in the nonmagnetic conductive layer by selectively etching the nonmagnetic conductive layer using a mask made of photoresist, forming a groove in the nonmagnetic layer by selectively etching a portion of the nonmagnetic layer exposed from the opening of the nonmagnetic conductive layer by reactive ion etching (hereinafter, also referred to as RIE), and forming the pole layer in this groove.
If formed by any of the methods disclosed in U.S. Pat. No. 6,710,973 B2, U.S. Patent Application Publication No. US2003/0151850 A1 and U.S. Patent Application Publication No. US2006/0077589 A1, the resultant pole layer has such a shape that, along the entire perimeter of the pole layer, the side surface of the pole layer is mostly inclined with respect to the direction perpendicular to the top surface of the substrate. The pole layer having such a shape is smaller in area of the cross section thereof perpendicular to the direction in which magnetic flux flows, as compared with a case where the entire side surface of the pole layer is perpendicular to the top surface of the substrate. The pole layer having the above-described shape cannot allow a magnetic flux of great magnitude to pass through a portion near the boundary between the track width defining portion and the wide portion, in particular. This results in degradation of the recording characteristics such as overwrite property. For this reason, in the pole layer having the above-described shape, the neck height must be reduced in order to suppress the degradation of the recording characteristics.
A portion of the side surface of the pole layer near the boundary between the track width defining portion and the wide portion is difficult to form accurately. Consequently, the portion of the pole layer near the boundary between the track width defining portion and the wide portion tends to have such a shape that the width gradually increases with increasing distance from the medium facing surface. Accordingly, as the neck height is reduced, it becomes difficult to accurately define the width of the track width defining portion in the medium facing surface, that is, the track width.
For the foregoing reasons, it has conventionally been difficult to form a pole layer that is capable of preventing the problems resulting from the skew, capable of defining the track width accurately, and capable of improving the recording characteristics.